Synchronous frame current regulators are employed for current control of AC motor/generators, such as three-phase permanent magnet synchronous electric motors (electric machines). By providing dynamic control over a wide frequency range, synchronous frame current regulators are suited to many industrial applications.
Control of AC motor/generators, such as three-phase permanent magnet synchronous electric motors (electric machines) is accomplished using a three-phase pulsewidth-modulated (PWM) inverter. A PWM inverter can be controlled in several different operation modes, including, e.g., a space vector PWM (SVPWM) mode and a six-step mode. Output voltage magnitude of the inverter at the fundamental frequency becomes its maximum only when an inverter operates in the six-step mode. Due to this voltage magnitude characteristic, operation in the six-step mode can increase torque capability of an electric machine compared to known SVPWM operation or discontinuous space vector PWM (DPWM) operation in the field-weakening region where the voltage magnitude is the major limiting factor of the torque capability. However, voltage magnitude is not controllable in the six-step mode. Only voltage angle can be adjusted in the six-step mode. This is equivalent to loss of 1 Degree-Of-Freedom (DOF) in controllability compared to operation in the normal SVPWM mode or the DPWM mode. Because of this DOF loss, it has proven challenging to employ an asynchronous frame current regulator with a PWM inverter operating in the six-step mode.